108. Convert Sorted Array to Binary Search Tree

/**32ms ac
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* sortedArrayToBST(vector<int>& nums) {
if(!nums.size()) return NULL;
int len = nums.size();
TreeNode* a=new TreeNode(nums[len/2]);
vector<int> nums1;
vector<int> nums2;
nums1.insert(nums1.end(),nums.begin(),nums.begin()+len/2);
nums2.insert(nums2.end(),nums.begin()+len/2+1,nums.end());
a->left=sortedArrayToBST(nums1);
a->right=sortedArrayToBST(nums2);
return a;
}
};